(a) Field of the Invention
The present invention relates to a display device, and more particularly, to an organic light emitting diode display.
(b) Description of the Related Art
Recently, lightweight and thin monitors and televisions are increasing in popularity, and liquid crystal displays (“LCDs”) which are relatively light and thin are being substituted for conventional cathode ray tubes (“CRTs”).
However, since the LCD is a passive light emitting device, a light source, such as a backlight or reflected sunlight, is required. LCDs also have many problems including slow response speed, a relatively small viewing angle, as well as other problems.
Recently, an organic light emitting diode (“OLED”) display is receiving increased attention as a display device which can overcome such problems.
An OLED display includes two electrodes and an emitting layer interposed therebetween. The light emitting layer receives an electron injected from an electrode and a hole injected from the other electrode. The electron and the hole are combined in the emitting layer to generate an exciton, which radiates energy, thereby emitting light.
Since an OLED display, which is itself a light emitting display device, does not require an additional light source, it has an excellent response speed, a wide viewing angle and a high contrast ratio, as well as lower power consumption.
However, an OLED display has different light emitting efficiencies according to the color of the light emitting materials. A typical OLED may include three or more differently colored light emitting materials, each with a different light emitting efficiency; e.g., a red light emitting material with a high degree of light emitting efficiency, a green light emitting material with a medium degree of light emitting efficiency, and a blue light emitting material with a low degree of light emitting efficiency. Therefore, in order to control the emission of red, green and blue light equally, displays are designed around pixels which have the lowest light emitting efficiency, and in such displays, the aperture ratio is remarkably deteriorated.
Therefore, an OLED display device with an increased aperture ratio which ensures current driving characteristics of an OLED display is desired.